1. Field of the Invention
The present invention relates to an infrared interferometer which may be mounted on aircrafts, satellites or the like for observation of atmospheric spectra, etc., and particularly to an interferometer which allows simultaneous correction to eliminate the influence of clouds.
2. Description of the Prior Art
Conventional approaches for atmospheric observation with an interferometer mounted on an aircraft, satellite or another flying body require a wide field of view and a sufficient amount of light flux to meet, for example, the requirement that both a high S/N ratio and high-spectral resolution be established simultaneously. Accordingly, the spatial resolutions of sensors for atmospheric observation are inferior to those of cameras for catching images of the earth's surface. In the case of such observation with sensors for atmospheric observation, there is a very high possibility that each pixel partially comprises a cloud. In addition, it is important to obtain information on the cloud coverage ratio (the ratio of the cloud present in each pixel) and the height of the top of the cloud (the height of the top surface of the cloud) for atmospheric observation since it is indispensable for making corrections to thereby eliminate the influence of the cloud.
An interferometer of the prior art which is mounted on aircrafts, artificial satellites or the like will now be explained with reference to FIG. 2. This type of interferometer comprises an infrared interferometer itself for observation of atmospheric spectra or the like and a cloud camera which uses a two-dimensional multi-element array detector for measurement of cloud distribution. First, the interferometer is constructed from a moving mirror 11, a fixed mirror 12, a beam splitter 13 and an interferometer detector 15. The incident light 14 from the subject of observation is separated by the beam splitter 13 into two beams directed to the moving mirror 11 and fixed mirror 12, respectively, which are then reflected by the respective mirrors to be modulated in interference light which is detected by the interferometer detector 15. On the other hand, the cloud camera comprises a cloud camera-detector 16 which is a two-dimensional multi-element array detector and a light-collecting optical system 17 which condenses light 18 incident from the subject of observation on the cloud camera-detector 16. The interferometer detector 15 is usually a single element, while the cloud camera-detector 16 is constructed and placed so that the image obtained by the single element is divided into fine, high-spatial-resolution images of the cloud.
Interferometers of the prior art which are mounted on satellites, etc., have the following drawbacks:
(1) The camera for measurement of cloud distribution is separated from the interferometer, and this construction increases the weight and size, for which reason the interferometer is not suitable for mounting on aircrafts, satellites, etc. In addition, the interferometer and camera may have different fields of view because of error in their mounting placement, and this difference interferes with making corrections to eliminate the influence of the cloud.
(2) The image captured by the camera only provides information regarding only whether a cloud is present or not in the pixel. Moreover, this information is not on spectra, and thus cannot be used to determine the height of the cloud.